Residual fractions and heavy oils obtained from the distillation of crude petroleum often contain substantial amounts of metals, such as nickel, vanadium, iron, copper and sodium, and have a high concentration of asphaltenes, polynuclear aromatics and other coke precursors. In a catalytic cracking process, particularly a fluidized process such as FCC, these metals and coke precursors significantly and adversely affect the cracking ability of the catalyst, and, over time, will poison and/or deactivate it. In order to render the heavy oil or residual fractions more suitable as feedstocks for FCC and hydrocracking processes, it is advantageous to pretreat the residual oils first, in the absence of hydrogen, to remove substantial portions of the metals and coke precursor contaminants. A typical pretreatment process involves contacting the high boiling oils with an inert, sorbent material exhibiting relatively low or no significant cracking activity, under conditions of time, temperature, and pressure sufficient to reduce the metals and Conradson carbon residue values of the residual oil feed to within more acceptable limits for downstream processing.
The art suggests many processes for the reduction of metals and coke precursors in residual and other contaminated oils, in the absence of added hydrogen. One such process is described in U.S. Pat. Nos. 4,243,514; 4,263,128; 4,311,580; 4,238,091; and 4,427,538, assigned to Engelhard, Minerals and Chemicals, Inc., which patents are incorporated herein by reference. The process described in the Engelhard patents is known in the art as the "Asphalt Residual Treating (ART) Process" and generally relates to the pretreating of residual oils to produce acceptable cracking stock for FCC-type units.
In that process, inert solids are introduced into a unit mechanistically similar to an FCC unit for the removal of metals and carbon contaminants. Those inert solids comprise a circulating inventory, which circulates from a reactor zone, where contaminants are deposited on the solid particles, to a regeneration zone where carbon-containing contaminants are removed from the inert material by thermal decomposition. The particles are then available for recycle back to the reaction zone. In the ART process, the claimed particles have a low surface area, i.e., less than about 100 m.sup.2 /g, preferably below 50 m.sup.2 /g, most preferably below 25 m.sup.2 /g and in actual practice around 10 to 15 m.sup.2 /g. The particles are ordinarily composed of kaolin or clay which has been spray dried into microspheres. For a specific description of this process, see in particular U.S. Pat. Nos. 4,263,128 and 4,243,514.
Many feeds however, particularly heavy feeds, also contain high levels of sulfur as an additional contaminant. In this process, the sulfur is converted to sulfur oxides, which are environmentally harmful pollutants and notoriously difficult to handle easily. In the prior art, this SO.sub.x problem is generally dealt with by removing it from the system and separately treating it. See, for example, U.S. Pat. No. 4,325,817. However, this is believed to be generally cumbersome and inefficient.
Cracking processes, particularly fluid catalytic cracking, also have SO.sub.x problems, and it is known in the art to use separate particles for the reduction of SO.sub.x emissions from them. In preferred processes, high surface area alumina is cycled between the FCC reactor zone and a regenerator zone. The alumina adsorbs the SO.sub.x, which is formed in the regeneration zone by the thermal decomposition of the sulfur-containing contaminants, from the catalyst particles. The SO.sub.x -containing alumina is then recycled to the reactor zone Where the reducing atmosphere converts the SO.sub.2 or SO.sub.3 to H.sub.2 S, which is subsequently removed and treated by conventional means. It is also known and preferred to use promoters for the promotion of SO.sub.2 to SO.sub.3, to take advantage of the enhanced ability of alumina to adsorb SO.sub.3 . Suitable examples of prior art processes in this area include U.S. Pat. Nos. 4,071,436; 4,115,250; and 4,544,645. The preferred alumina in these prior art processes is a high surface area active alumina, suitable for the adsorption of SO.sub.x.